Process of plating aluminum.



UNITED STATES PATENT OFFICE.

JOSEPH A. HALL, 0 NEW BRITAIN, CONNECTICUT.

PROCESS OF PLATING ALUMINUM.

No Drawing.

T0117] 'NllOl/I it may concern l e it known that I. Josnrn A. IIALL, a. citizen of the l nited States, residing at New Britain. in the county of Hartford and State of Connecticut, have invented certain new and useful Improvements in Processes of llating Aluminum, of which the following is a specification.

My invention relates to improvements in processes of plating aluminum, and the object of my improvement is to produce a process of plating that is commercially practicable: that can be applied to the plating of aluminum with brass. copper, silver, and nickel. and that furthermore can be applied to the plating of commercial aluminum, such as is found in use in ordinary arts and manut'm-tures. as distinguished from such aluminum as may be chemically pure and which may be found new and then to some extent in the lalmratory. In the treatment for plating of such chemically pure aluminum some of the steps to my process to be described may he omitted, as being unnecessary. However, as my process is adapted to successful operation with aluminum of either kind or both kinds, that is. either commercial or chemically pure, I believe the same to be properly termed as a process of plating aluminum. Accordingly. my process is safe and proper to use in any case, and particuhirly in cases where there may be doubt as to the grade and quality of the aluminum to be plated.

in carrying out my process, first treat the surface of the aluminum to be plated to a preliminary cleansing operation, which I prefer to consist in washing first with benzin and then in a solution of caustic soda. This preliminary cleansing operation is ordinary. and serves to remove grease and foreign matter that may be adhering to the surface.

The preliminary cleansing operation or step described is followed by a. special cleansing step. in which the material is dipped in a bright dip made up of 2 parts of nitric acid and 1 part oil of vitriol and rinsed. The purpose of the bright dip treatment is to rei'nove from the surface all metallic particles other than aluminum. The importance of this step I find to lie in the fact that 1 have found that there is present in most cases on the surface of aluminum as ordinarily found in the arts an appreciable quantity of particles of iron, these particles Specification of Letters Patent.

Patented July 27, 1915.

Application filed February 5, 1915. Serial No. 6,377.

being present to a sufiicient extent to interfere with and actually prevent the successful carrying out of the succeeding steps or stages of my process, and I believe that the presence of this iron has been one of the obstacles in the way of the successful plating of aluminum heretofore.

It will be noted that the solution of the bright dip mentioned is relatively strong in nitric acid. This is the condition that I firefer and good results can be obtained by my process by omitting the oil of vitriol altogether, using the nitric acid alone.

After the two cleansing stages described the material is subjected to the first step in the plating process proper, and which consists in plating the surface with zinc by the electro-deposition process. For this purpose. I prefer to use a strictly zinc solution, though in some cases a brass solution may be used that is high in zinc. In case a brass solution is used for this stage the brass should be so high in zinc as to show no brass color.

The zinc plating sufficient for my purpose. and which is to coat the surface with a thin film of zinc, I find to be readily effected in a few seconds.

After the zinc plating described the surface is ready for the regular solution for plating with such materials as brass, copper, and silver, and in applying the. said materials in most cases the plating will be continued for a few hours. In case of plating with nickel however I find that the direct plating of nickel on the zinc to be, inoperative, as the solution has acid qualities, so that the same would attack the surface of the Zinc injuriously.

I find that plating with nickel can be successfully effected by first coating the material with a plated coating of copper, involving however a treatment in the copper solution of. only 20 to 30 minutes, instead of the usual 2 or 3 hours that is required to ob tain a finished coating of cop-per. After the surface has been coated with copper in the manner described the nickel. plating is applied essentially in an ordinary manner.

Articles that have been plated by my castings, which is high in aluminum, but contains an appreciable quantity of other material. 7 For the solution used for the bright dip, in the special cleansing step, the nitric acid may have a density corresponding to a reading of 36 to 40 on the hydrometer, and oil of vitriol may be quite Weak, as this ingredient may in some cases be dispensed with and still permit of obtaining satisfactory results. One gallon, of nitric acid is used to 2 quarts of Water.

In the zinc electro-deposition stage the zinc salt used in the solution is zinc carbonate. The solution is made up of 1 gallon of Water to 1 pound of cyanid of soda and 6 ounces of zinc carbonate, standing atabout 9 on the hydrometer.

The nickel solution is made up of one gal v lon of Water to 8 ounces of nickel ammonium sulfate, 2 ounces of nickel sulfate, and 1 ounce of ammonia, and stands at about-5 on the hydrometer.

The solutions described I find to be par ticularly stable, so that my process can be continuously maintained, and by persons of limited experience, and given a few simple y directions.

In order to maintain the constancy of the that is relatively strong in nitric acid, plating the surface so cleansed by the electrodeposition process for a few seconds in a. zinc bath containing cyanid of soda and zinc carbonate, and then applying to the surface of the zinc a coating of some metal other than zinc.

2. The process of plating articles of aluminum comprising removing foreign particles from the surface ofv the aluminum, electroplating the'said surface in a bath containing cyanid of soda and zinc carbonate, and then plating the zinc surface with metal other than zinc.

JOSEPH A. HALL.

Witnesses:

WM. F. RoDMAN, ALFRr-n L. THOMPSON. 

